(a) Field of the Invention
Broadly speaking, this invention relates to lasers. More particularly, in a preferred embodiment, this invention relates to methods and apparatus for measuring the intensity of the side lobes in a laser beam.
(b) Discussion of the Prior Art
In apparatus using solid state lasers, the presence of relatively strong side lobe beams gives erroneous data, which may lead to a degradation of the system performance. It is, therefore, important to be able to select lasers with low sidebeam intensities.
In conventional tests of laser beam intensity, the laser beam is typically directed toward a diffuse reflector, for example, magnesium oxide or barium sulphate. The surface normal and the laser beam direction are made collinear. At a small angle from the surface normal, and at some convenient distance, a detector system, with known response characteristics, is used to determine the laser beam energy and/or the laser beam power. If the angular separation between the side lobes and the main beam is small, the side-lobe beams can be relfected off the diffuse reflector which leads to an erroneous interpretation of the main beam energy. If the angular separation between the side lobes and the main beam is large, the side lobes are not reflected from the diffuse reflector, but their generally unknown direction prevents measurement of their beam energies. This is particularly true for high-intensity, short-duration laser pulses in a spectral region where the radiation evokes little or no visible response, but can cause physiological damage to the unprotected eye.